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In all versions of Windows 9x except ME, it is also possible to load Windows by booting to a DOS prompt and typing "win". There are some command line switches that can be used with the WIN command: with the /D switch, Windows boots to safe mode, and with the /D:n switch, Windows boots to safe mode
The upper part is accessible only from kernel mode, and with some exceptions, is instantiated just once, system-wide. ntoskrnl.exe is mapped into this region, as are several other kernel mode components. This region also contains data used by kernel mode code, such as the kernel mode heaps and the file system cache.
On Apple Mac computers using Intel x86-64 processor architecture, the EFI system partition is initially left blank and unused for booting into macOS. [13] [14]However, the EFI system partition is used as a staging area for firmware updates [15] and for the Microsoft Windows bootloader for Mac computers configured to boot into a Windows partition using Boot Camp.
The boot loader; performs basic system initialization options such as loading the hardware abstraction layer and boot-time device drivers, prior to passing control to the Windows kernel. In versions prior to Vista, NTLDR and IA64ldr also display menus to the user if multiple operating systems are defined in boot.ini, or if F8 is pressed.
[10] The reset vector for MIPS32 processors is at virtual address 0xBFC00000, [11] which is located in the last 4 Mbytes of the KSEG1 non-cacheable region of memory. [12] The core enters kernel mode both at reset and when an exception is recognized, hence able to map the virtual address to physical address. [13]
The Windows NT kernel is a hybrid kernel; the architecture comprises a simple kernel, hardware abstraction layer (HAL), drivers, and a range of services (collectively named Executive), which all exist in kernel mode. [1] User mode in Windows NT is made of subsystems capable of passing I/O requests to the appropriate kernel mode device drivers ...
When called from ntdll.dll in user mode, these groups are almost exactly the same; they execute an interrupt into kernel mode and call the equivalent function in ntoskrnl.exe via the SSDT. When calling the functions directly in ntoskrnl.exe (only possible in kernel mode), the Zw variants ensure kernel mode, whereas the Nt variants do not. [ 1 ]
A modern computer operating system usually uses virtual memory to provide separate address spaces or separate regions of a single address space, called user space and kernel space. [ 1 ] [ a ] Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour.